1. Field of the Invention
This invention relates to a method of controlling a device for the contact toughening of glass sheets, comprising a horizontal furnace for heating glass sheets, a press containing two liquid-cooled pressing plates, a feed apparatus for transferring the heated glass sheets into the press and a device for removing the glass sheets from the press. The invention furthermore relates to apparatuses for carrying out this method.
2. Discussion of the Related Art
Usually, the toughening of glass sheets is performed by blowing cold air streams onto the glass sheets heated to a toughening temperature. During the toughening treatment, the glass sheet is either held in a vertical position by tongs which grip the upper edge of the glass sheet, or the glass sheet rests in a horizontal orientation with its edge on a support ring. If, with the abrupt cooling by air, a glass sheet shatters, the glass fragments fall unimpeded, for example into a fragment container disposed underneath the toughening apparatus. The rhythm of the toughening process is therefore not adversely affected or interrupted during continuing production.
In the case of so-called contact toughening, the sudden cooling of the glass sheets, heated to toughening temperature, takes place by the intensive contact of the hot glass sheets with the water-cooled surfaces of two pressing plates of a press. Devices for contact toughening are, for example, known from DE-OS 1 771 7909, EP 0 277 074 B1 and DE 4 019 181 A1. The pressing plates may also be constructed as bending molds. In this manner it is possible simultaneously to bend the glass sheets heated to toughening temperature to a desired shape and to toughen them. This method has, compared with the usual air toughening, the advantage that by the direct contact with the pressing plates, it is possible to avoid deformations or distortions of the glass sheet that can occur in certain circumstances, when the glass sheet during air toughening is held only at the edge or on one face.
The contact toughening is carried out in a horizontal position of the glass sheets, because the glass sheets must come into contact over their entire surface with the pressing plates. If, in contact toughening, a glass sheet shatters, the glass fragments consequently remain completely or at least partly resting on the lower pressing plate. Before the next glass sheet, heated to toughening temperature, can be laid on the lower pressing plate, this pressing plate must be completely cleared of the glass fragments. Otherwise, in contact toughening of the next glass sheets, damage to the surfaces of the pressing plates and to the glass sheet itself will occur.